Sorry - coming in late to this on a Sunday. But, the black channel indicates a dirty head. Cyan as well. This would not come from humidity but rather possibly a dirty capping station, over saturated pads, dirty or worn wiper blade, in general an unclean cleaning station that is foaming and not draining well and the bubbles of foam are probably adhering to the print head after the final wipe. Your nozzles are mis-directed in many cases. Almost looks like electrical. Without having to go back through all of your experience - have you cleaned the capping station of this printer and the wiper blade? Did you inspect the wiper blade> is it pitted or worn? They are cheap to replace. Are you the person with the draining 2880 carts? If so - then the capping station may be wicking them.
In any event - your black is definitely a pattern of a dirty print head or a too wet print head from the cleaning station. Look at the lines as they are formed irregularly. As the print head moves it fires a few drops out each nozzle. This is happening in micro seconds and in the time it takes to shoot the ink out it is bending. This is usually indicated by two things: 1) electrical 2) dirty print head (thin film of ink still smeared on the head instead of it being wiped clean by the squeegee wiper blade). Electrical would be also spraying ink where it is not intended (like in the margins).
Magenta bleeding into Yellow indicates the capping station seal is leaking and the Yellow is sucking up the magenta rather than the being pulled down into the capping station. This is very common on a roland printer and indicates time to replace the capping station. The rolands are powered by six individual epson heads and six individual capping stations. Each head has two different colors in it. When one sucks up the other color you change the capping station ($12) and back in the race. But you can actually watch the head cleaning on a roland and see whether it is foaming. On the Epson they keep that under the plastic and hard to get an eyeball on it. On the rolands you replace the wiper blades every liter or so. They pop out and you are directed to replace them. The principle is the same - keeping the epson print heads wiped clean. Any ink film will misdirect the ink or prevent it from being ejected. Likewise with too little or too much humidity drying the orifices or allowing them to be too wet. But yours looks like typical capping station.
When a printer is used over a long period of time the capping station may not drain so easily because of what is beneath the pad and the tubing that goes to the waste pads at the bottom of the printer. That needs to drain nearly instantly as it would with a new printer. Otherwise it foams when it sucks through the print head. When the head moves into position to get wiped by the wiper blade it does not fully clear the capping station foamy bubbles and they adhere as the final step. So the wiper blade is not able to do its mission.
In your case, it might be worth it to really clean the pad and the drain tubes. You may have some gunk buildup over time.
Not certain what else you can do. If you are thinking OEM - go ahead and buy a set of carts and use them. If the problem is remaining - clean your printer or service and replace the cleaning area.
If the problem goes away - try a different set of cartridges with the ConeColor. Your carts could be draining but the R2880 is a good machine and the cartridges we sell are what I use at the workshops in Santa Fe as well as for ink testing in R&D. We run 5 R2880s at the Santa Fe workshop. They are a little slow to come up after sitting for five months - but we use the heck out of them running about 50 sets of cartridges over 5 days. We maintain the capping station and wiper blades as part of the workshop demonstrating printer maintenance. So they get cleaned properly twice a year.
Another suggestions: you should be able to put a few drops of PiezoFlush on the pads in the cleaning station and watch it swell just for a second and then drain. If it swells but drains very slowly - then dig deeper into the cleaning station and get to the tubing. The part that drains into the tube or the tube itself may also be preventing the movement of the sucked out ink down to the waste pads or out into the bottle if you are using an external waste bottle.
But magenta into the yellow is a dead give away that there is a problem in your capping station during cleaning. You got to deal with that.
Also if all of this has already been suggested to you and you have done all of this - you may have reassembled the capping station and it is slightly raised so as the normal wet swelling of it during a clean cycle is reaching the print head.
Hope I do not feel like an idiot and read back and see that you have been through all of this alreadyā¦ so I wonāt. I think the suggestions I am making are valid for what you are describing as well as the image you just posted. Will check in later today to see for a reply.
best,
Jon